1. Field of the Invention
The present invention relates to a hydraulic control system and method for an automatic transmission used in a vehicle; and, more particularly, to a technique for avoiding generating a shock in the automatic transmission when a gear is shifted from a neutral position to a reverse position.
2. Background of the Invention
Japanese Patent Application Publication No. 2005-273879 describes an automatic transmission for a vehicle that includes a first-gear step and reverse gear step engagement element used for establishing a first gear step and a reverse gear step, which can enter any of a plurality of shift gear steps having different transmission gear ratios by selectively engaging a plurality of engagement elements. In this automatic transmission, when a gear selection device is shifted to the reverse position (R position), a reverse range pressure (R-range pressure) supplied from a manual valve is exerted on the first-gear step and reverse gear step engagement element as an original pressure thereof. However, when the gear selection device is shifted to the neutral position (N position), the first-gear step and reverse gear step engagement element becomes disengaged.
However, in the above-described hydraulic control system, when the gear selection device is shifted from the N position to the R position when the vehicle is stopped, the R-range pressure is directly applied to the first-gear step and reverse gear step engagement element without being pressure-regulated or flow-rate-controlled. Thus, the first-gear step and reverse gear step engagement element may be brought into a quick engagement, so that rotary elements of the automatic transmission having high rotational inertia, such as drums or ring gears, which have been rotated in conjunction, may be abruptly stopped, thereby generating a shock in the automatic transmission.